Overview of Visual Systems

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label: anatomy of the eye
Describe the vision acuity of this individual: Emmetropia (normal)
Describe the vision of this individual: Myopia (nearsighted)
Describe the vision of this individual: Hyperopia (Farsightedness)
Describe the pathway light takes as it moves through the layers of the eye: Nerve fiber layer
Ganglion cell layer
Inner Plexiform Layer
Inner Nuclear Layer
Outer Plexiform Layer
Outer Nuclear Layer
Photoreceptors
Pigment Epithelium
Label the different components of the diagram: Components
Label the portions of the visual pathway: Answers
Which reflex is this? Label the parts: The Pupillary Reflex
Which reflex follows a similar pathway to the pupillary reflex?: The accomodation /
convergence reflex
Describe the shape of an accommodated lens.: The lens increases in diameter and approaches a round shape.
Fill in the blanks: Answers
Describe Macular Sparing and the theories behind it.: Macular Sparing is due to a cortical lesion
Two theories:
1. Macula occupies a large amount of primary visual cortex: therefore in a cortical lesion it is likely that part will be spared.
1. Watershed region: dual blood supply allows sparing
What are the 3 main layers of the eye?: 1. Sclera/Cornea
2. Uveal Tract (Choroid, ciliary body and iris)
3. Retina
What are the 3 chambers of the eye? Which chamber is the largest?: 1. Anterior aqueous humor
2. Posterior aqueous humor
3. Vitreous humor
The vitreous humor is the largest
Which layer of the eye is avascular?: The cornea
The sclera and the cornea are for the most part continuous. Where does each begin and end?: The sclera surrounds the posterior 5/6ths of the eyeball. The cornea, then, surrounds 1/6th of the eyeball.
Define the following components of the sclera: 1. Suprachoroidal Lamina 2. Tenon's space: 1. melanocytes in loose CT
2. detached region of the sclera at the sclera-cornea junction
What are the 5 layers of the cornea?: From outer to inner:
1. Epithelium - stratified squamous
2. Bowman's membrane
3. Stroma
4. Descemet's membrane
5. Endothelium - simple squamous
The uveal tract is divided into 3 regions. What are they?: 1. Choroid
2. Ciliary Body
3. Iris
What is the choroid made of and what is found in this material?: A loose CT matrix that contains fibroblasts, melanocytes, lymphoid cells
What is the layer of the choroid that nourishes the retina called?: Choriocapillary layer
What is the name of the membrane that acts as a barrier between the choroid and the retina?: Bruch's membrane
The ciliary body is actually a ________ that has extensions called _________.: Ciliary muscle, ciliary processes
What is the function of the ciliary processes?: Anchors lens and aids in lens accommodation
Accommodation is _________ focusing while the iris controls _______ focusing.: fine, coarse
What is the function of ciliary epithelium?: secrete aqueous humor of anterior and posterior chamber
The sympathetic nervous system innervates which pupillary muscle?: dilator pupillae
The parasympathetic nervous system innervates which pupillary muscle?: sphincter pupillae
Label the layers of the lens Give a characteristic of each: 1. Lens Capsule - thick basal lamina
2. Subcapsular epithelium - "stem cell" (regenerating) cell layer of the lens
3. Lens fibers - filled with crystallin protien that refracts light
What are the 3 layers of the retina? What is found in each layer?: From outer to inner:
1. outer layer - photoreceptor cells
2. middle layer - bipolar neurons
3. inner layer - ganglion neurons from optic nerve
What is this a slide of? Name the layers: Retina
Answers
Where are Muller cells found? What is their function?: The retina - they are specialized astrocytes that form the internal and external limiting membranes
Name the non-nuclear layers of the Retina.: Answers
How many rods are in the average retina and where are they located within the retina?: ~120 million
more concentrated along the edges of the retina
Which are extremely light sensitive: rods or cones?: Rods - they see black & white and are used in night vision
What is rhodopsin and where is it found?: photopigment; found in disks of rod cells
How many cones are in the average retina and where are they located within the retina?: ~6 million (less than rods)
more concentrated along back of retina and fovea
Which are extremely color sensitive: rods or cones?: cones
What is an amacrine cell and where is it found?: Various neurons in the retina: they synapse with different photoreceptors. function not understood
What is a Limbus and where is it found?: trabecular meshwork at corneoscleral junction; contains canal of Schlemm
How does aqueous humor drain from the anterior chamber into the episcleral vasculature?: Via the canal of Schlemm
What are the components of the vitreous humor?: H2O - 99%, collagen, hyaluronic acid molecules
There are no ___________ at the blind spot. What is another name for the blind spot?: photoreceptors
Optic papilla or optic disc is another name
What are the glands of Moll and Zeis and where are they found?: both found in eyelid
Moll - sweat gland
Zeis - sebaceous gland
Which cells make synaptic contact in the outer plexiform layer of the retina?: photoreceptors, bipolar and horizontal cells
Which cells make synaptic contact in the inner plexiform layer of the retina?: bipolar, amacrine, ganglion cells
[cGMP] is ________ (high/low) in the photoreceptor cell in the dark.: high (photoreceptors are activated at in the dark: cGMP keeps the ion channels open)
Light closes cation channels to inactivate the photoreceptors. They are closed in a 3 step process - what is it?: 1. Light activates pigment molecules in disc membrane
2. activated pigment stimulates a G-protein. THis G-protein activates cGMP phosphodiesterase (which breaks down cGMP)
3. as cellular [cGMP] is lowered the channels close. This reduces the inward cation current and the cell hyperpolarizes.
light coming from the right visual field is projected onto the ________ portion of the left retina and the _______ portion of the right retina.: temporal
nasal
The fovea is always ________ to the optic disc: lateral
Where does the fovea sit in the visual field? Where does the blind spot sit in the visual field?: In the center
slightly lateral to the fovea
The Lateral Geniculate Nucleus (LGN) is found _______.: in the posterior portion of the thalamus
Where does the 1st synapse in the visual pathway occur?: At the LGN
Optic fibers associated with the fovea project onto the ________.: posterior calcarine cortex
Meyers loop contains ________ visual fields which project ____________.: superior
on the inferior calcarine fissure.
The _______________ portions of the visual field stay ipsilateral, whereas the ___________ portions of the visual field cross at the _________.: Temporal
Nasal
Optic Chiasm
Pupillary light reflex: 1. receptors? 2. afferent limb? 3. CNS center? 4. efferent limb? 5. peripheral effector?: 1. photoreceptors
2. CN II
3. pretectal area (tectal=midbrain)& Edinger-Westphal nuclei.
4. CN III
5. sphincter pupillae (bilaterally)
Is there a decussation in the pupillary light reflex? If so, where is it?: Yes. In the CNS (pretectal area and E-W nuclei)
Information decussates here b/c there is bilateral projection from the pretectal area to the E-W nuclei via the posterior commissure)
The Accommodation reflex: 1. Receptors? 2. Afferent Limb? 3. CNS centers? 4. Efferent Limb? 5. Peripheral Effector?: 1. photoreceptors
2. CN II
3. Lateral Geniculate Body, primary visual cortex, E-W nuclei
4. CN III
5. sphincter pupillae muscle (pupillary constriction) and ciliary body muscle (lens accommodation)
When the ciliary body muscles are contracted what happens to the lens? Why?: The lens gets fatter. Tightening the ciliary body muscle releases tension on the suspensory ligaments of the lens: this allows the lens to fatten
To see far away how is your lens shaped? To see close up how is your lens shaped?: far away --> stretched out and thin
close up --> fat
What is an Argyll-Robertson pupil? What is it a sign of?: pupils are:
small
don't react to light
DO constrict on accommodation
A sign of neurosyphilis
What is Horner's syndrome?: any damage to sympathetic pathways in either the brainstem, intermediolateral cell column or superior cervical ganglion.
How does a lesion in descending sympathetics present?: 1. ptosis (drooping eyelid)
2. miosis (constricted, fixed pupil)
3. anhydrosis (no sweating on ipsilateral face)
The sympathetic pathway has 3 synapses. Where are they?: 1. brainstem (hypothalamus)
2. intermediolateral cell column in an upper thoracic spinal cord segment
3. superior cervical ganglion
The smooth muscle elevator of the eyelid is ___________ active.: tonically
What is the major function of the superior colliculus?: Integration of visual, auditory and somatosensory information resulting in orientation to a particular stimulus. Can be via head, eye or neck movements.
Where does the tectospinal pathway originate?: the superior colliculus; it is a descending motor pathway
If a visual field defect was only in one eye, where would the lesion be?: In the optic nerve of the affected eye (before the optic chiasm)
scotoma: an area within the visual field where vision is absent or depressed. (artificial BLIND SPOT)
anopia: complete loss of vision in one or both eyes
hemianopia: loss of vision in one half of the visual field of one or both eyes
homonymous hemianopia: hemianopia restricted to one visual field (L or R)
heteronymous hemianopia: loss of vision in opposite halves of the visual field. (ie. bilateral temporal field is lost)
quadrantanopia: loss of vision in a quadrant of a visual field
Meyer's loop carries information from which visual field? Where does it project?: Superior visual field
Projects to the inferior calcarine cortex
Fibers from the inferior visual fields project where?: Superior calcarine cortex
Function of Tectospinal Pathway?: Controls neurons that innervate proximal and axial musculature (common function - orient head to sensory stimulus)
Blood supply to primary visual cortex? Blood supply to macula's area on the primary visual cortex?: PCA (Posterior Cerebral Artery)
Macula has both MCA and PCA
What is iodopsin and where is it found?: iodopsin is the photopigment used by cone photoreceptors.
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